sleeping bag 'science'

2:52 p.m. on January 10, 2018 (EST)
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i enjoyed this article about differing views for keeping warm while you sleep. some people layer inside a sleeping bag, some go the bare minimum route, others in between.  https://www.outsideonline.com/2271191/how-experts-layer-sleeping-bag 

i agree with comments in the article that you need to think about keeping warm in the outdoors systemically. without adequate insulation below the bag, you will bleed a lot of heat. layering inside a bag depends on how warm or cold you sleep, how well-insulated your sleeping bag is, how much room you have inside the sleeping bag to layer without compressing the insulation, and what happens to moisture your body naturally emits while you sleep, particularly in the winter because that natural vapor you send out can freeze in the outer layers of your sleeping bag insulation, hurting loft and limiting the effectiveness of the insulation.  

it is very important to me to be able to lie inside a sleeping bag when i'm shopping, for these reasons. some bags (Valandre makes a few prime examples, like the shocking blue and bloody mary) are sized to be used in combination with a good down jacket, very roomy inside, leaving space for a lofty layer inside. others, you wear a down jacket in the bag & feel like an anaconda python just swallowed you - and if the insulation is compressed, you aren't going to feel as warm inside the bag.  

i have been happy using both down and synthetic fill bags in the winter, been happy at 25 to 30 below in both. a good winter bag occupies an inordinate amount of space in a backpack regardless, but the main difference was that the synthetic fill bag was truly massive and harder to compress for storage. the synthetic was good to those low temperatures, in part, because it was quite roomy, so i would sleep in a down sweater or jacket to augment the bag. the down bag is fine but not nearly as roomy, so i generally sleep in that with a light base layer, socks and a beanie.  when i was taking longer trips in the cold, i used a VBL liner, slept in a light base layer.  

11:16 a.m. on January 11, 2018 (EST)
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Insulation from the ground to stop conduction, and wear a warm hat. 

11:04 p.m. on January 12, 2018 (EST)
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I think this really just depends on what rating your bag has and what the temperature is.

Yes, if you're going into a night where the temperature will be hitting single digits and below, you should wear some baselayers unless you have some crazy -40 sleeping bag. These will help generate heat throughout the night for the drop in temperatures. If your body just runs not as hot normally, some baselayers and a beanie will help.

If you're heading into some warmers nights around 20 or 30, I myself always opt to sleep in my undergarments and call it good with my 15 degrees sleeping bag. I usually wake up just fine in those temperatures. 

Just plan and adapt to your situations accordingly. 

7:05 a.m. on January 13, 2018 (EST)
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layering to much or to little is the biggest test..Many people don't realize what kind of sleeper they are..I prefer not to have socks on my feet when I sleep so down booties ark well less constrictive. But we do have to take the bags temp rating into account...You thinking your going to be warm in 20 degree night or single digits with a 40 degree bag is just not going to happen...

2:48 a.m. on January 16, 2018 (EST)
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If I need to sleep in my bag (versus on top of it), I always wear long johns and socks.  This skin layer is used exclusively for sleep; I carry a second set of skin layers if the season warrants daytime wear of long johns.  If cool enough I also don a balaclava to bed; otherwise I lay my head on a t-shirt.  While skin layers can add warmth, they also serve to protect the bag from accumulating body oils and dirt.  I have several well used ten year old bags that I have never washed; regardless of this practice they have no human odors whatsoever.  And as we all know the less you have to mess with your bag accordingly, the longer it retains its loft.

When temps are so high that even my slumber party weight bag is too warm, I'll opt for just a cotton sheet (for example spring desert camping or hiking CGNP along the Tonto plateau.  In cooler temps down to freezing I'll wear additional layers to bed, if my bag is not warm enough.  But below freezing I place these layers on top of the bag instead of wearing them inside.  The reasoning behind this approach is making the entire bag warmer, thus pushing the frost line to beyond the bag's loft, into or onto the auxiliary layers.  Then when first emerging from the bag I compress the bag into tis stuff sack to expel whatever moisture is trapped within.  But this needs to be done before the bag losses body heat; otherwise the entrapped moisture will freeze up in the bag's loft.

If day time temps aren't expected to climb above freezing I'll bring a VP  layer for use inside the bag.  Some people also use an additional VBL on the outside of the bag in colder weather to minimize moisture from external air sources condensing in the loft. 

As for insulation from the ground I use an air mat, good enough for me down to 10 F, but for lower temps I'll add a winter duty blue foam pad (the foam pad is also a back up in case the air mat leaks and cannot be field repaired.

As for preferred bag filling, I always go with down for below freezing temps, or when rain is an issue.  When rain is a concern, I go with synthetic bags.  I have three down bags to cover below freezing temps with the coldest bag covering me to -25⁰F (I am too old to enjoy anything colder nowadays).  Above 20⁰ F I have both synthetic and down bags to cover all temps up to 45 F, and above that I use synthetic bags exclusively.

There is much talk about brand reputations, but for the most part any decent bag will hold up to nominal use.  As for rating the warmth, some brands are warmer than others, especially if you go by weight rather than advertised performance.  Some may find the relative roominess or snugness of bags an issue, but you can quickly assess this in the showroom.  What I find critical to sleep time satisfaction is how well the zippers perform!  Nothing is more aggravating than an snagged zipper at 3am when you need to pee or are trying to warm back up after a night trip to the bushes.  (I prefer to not use a pee bottle, except in bitter cold or stormy weather.)  So test the heck out of the zippers before you buy! 

Ed

January 16, 2018
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